Fluid Processing Apparatus

ABSTRACT

A machine is provided with a slot to releasably receive and retain a cartridge in which dialysis is effected. The machine is configured for supplying to the cartridge, at a controlled temperature and rate, sterile water for use in haemodialysis and is operable to maintain, in a sterile condition, residual water contained therein after completion of a haemodialysis treatment.

This invention relates to apparatus for the extracorporeal processing ofbodily fluids, in particular the extracorporeal dialysis of blood.

Most dialysis apparatus currently in use must be very rigorously cleanedbetween uses to prevent contamination, either cross-contamination fromone fluid to another or contamination, with for example bacteria, due topoor sanitation. This is particularly important in haemodialysis, whichcomprises removing blood from the body, processing it by means ofdiffusion exchange through a membrane with a dialysis solution, and thenreturning it to the body. In attempt to reduce the amount of cleaningrequired, various methods and apparatus have been developed whichutilize disposable single-use processing systems.

In these, and in other medical procedures employing disposable fluidprocessing systems, it is typical for the operator, who may be a trainedmedical professional, to first select and locate an appropriate filteror membrane element and one or more flow sets. These items must then beremoved from their sterile packaging and be connected together to form afluid circuit, which is then installed on the particular processingapparatus with which the procedure is to be performed. Typically, theprocessing apparatus includes multiple pump, valve, detection andclamping elements which interact with various parts of the disposablecircuit and which are operable to perform the process.

Previous designs to simplify the set up of such processes have proposedthat some of the fluid circuit elements be contained in a disposable“cartridge” which can be interfaced with a re-usable machine. Oftenthese systems have been complex requiring either a disposable flexiblebag-like circuit to be placed in a non-disposable rigid supportingstructure prior to inserting into the machine or requiring tubes to beconnected to various elements of a non-disposable component prior tointerfacing with the machine. While these designs go some way toproviding a solution to the cleaning problem, they are complex and thereis scope for error in their use. In haemodialysis in particular, thereare two fluid circuits, namely the blood circuit and the processingfluid (i.e. dialysis solution) circuit and while, in the priorproposals, the disposable component includes the full circuit for theblood, the processing fluid is supplied from a re-usable machine. Theprocessing fluid is typically supplied to the cartridge in one of twoways. The first is that large volumes of the sterile process fluid,namely water, containing various additional components, for examplesodium bicarbonate, is supplied to the machine. These volumes must bekept under specific conditions and can only be stored for a finiteamount of time before bacterial growth begins. In addition, if differentpatients require the use of different processing fluids this does notprovide a universal system. The alternative solution is that the machineis provided with a supply of de-ionised water (commonly in a medicalestablishment this will be produced centrally and then piped toapplications requiring it). The water is then heated in the machine to atemperature at which bacteria are killed and then cooled down tosubstantially the same temperature as the bodily fluid and then variousadditives are added to provide the required process fluid. When themachine is dormant between uses with this system it is necessary tosterilize all of the internal fluid lines within the apparatus betweenuses and consequently, although the system hygiene is improved by theuse of disposable parts and the set up is partially simplified for theoperator, the down-time between treatments is not reduced because of thecleaning process that is still required. Further, the machine complexityhas remained high because of the need to provide the chemical andcirculatory fluid paths required for the cleaning process.

Accordingly it is an object of the present invention to provide animproved haemodialysis apparatus wherein the need for cleaning iseliminated or minimised. According to the present invention there isprovided a machine adapted to releasably receive a cartridge in whichdialysis is effected, said machine having means for supplying to thecartridge, at a controlled temperature and rate, sterile water for usein the haemodialysis, the machine being operable to maintain in asterile condition residual water contained therein after completion of ahaemodialysis treatment.

Preferably the machine further comprises a water inlet, for receivingwater from a water supply, and a sterile water outlet, for supplyingwater to a cartridge, wherein said machine is provided with means forsterilising water as it flows from said water inlet to said sterilewater outlet.

Preferably the machine is provided with means for recycling the residualwater in a closed loop circuit through the means for sterilising saidwater when the apparatus is not performing haemodialysis of a patient'sblood, thus maintaining the residual water in a sterile condition.

In a preferred arrangement the means for sterilising the water comprisesmeans for heating the water to an elevated temperature at which at leastmicro-organisms and bacteria within the water are destroyed. Morepreferably the water is heated to at least 85 degrees centigrade.Preferably, subsequent to heating the water to sterilise it, saidmachine is provided with means to cool the water to substantially bodytemperature.

In an alternative preferred arrangement the method of sterilisation maybe an alternative known technique, for example irradiation techniquesmay be used.

Preferably the machine further comprises valve means for preventingwater from exiting the sterile water outlet when no cartridge ispresent.

Preferably the machine further comprises two platens, at least one ofwhich is movable in relation to the another, adapted to receive and holda cartridge in which dialysis is effected therebetween. Preferably theplatens comprise means that operate on, eg actuate valves and pumpsembodied in, the cartridge during haemodialysis.

In a preferred arrangement the sterile water outlet comprises an outletvalve in one of said platens which, when in a first position, presents aflush surface with said platen and prevents water from exiting thesterile outlet and a second position wherein an outlet is formed in theface of the platen allowing the sterile water to pass therethrough.Preferably when the outlet valve is in its first position residual waterwithin the machine is prevented by said outlet valve means from exitingthe sterile water outlet, and is circulated around a closed loop withinsaid machine, said closed loop passing the water through the means forsterilising the water, thereby maintaining the residual water in asterile condition.

Preferably when a cartridge is not present between said platens, theplatens sealingly engage against one another such that the water exitssaid sterile water outlet and is circulated through the platens andthrough the means for sterilising the water in a closed loop within saidmachine, thereby maintaining the residual water in a sterile condition.

According to a second aspect of the invention there is provided anapparatus for performing haemodialysis of a patient's blood, theapparatus comprising:

a) a cartridge in which dialysis is effected, the cartridge beingconnectable by tubing to the patient's blood circulatory system; andb) a machine as described above.

In a preferred arrangement, when the means for sterilising the watercomprises means for heating the water to an elevated temperature atwhich at least micro-organisms and bacteria within the water aredestroyed, subsequent to heating the water to sterilise it, the waterexits the sterile outlet at an elevated temperature and is cooled tosubstantially body temperature within the cartridge.

Preferably the cartridge comprises various pumps and valves and themachine comprises two platens, at least one of which is movable inrelation to the another, in between which the cartridge is held duringuse and said platens comprise means of actuating said various pumps andvalves.

In a preferred arrangement the sterile water outlet interfaces with theedge of the cartridge.

In a preferred arrangement, when the cartridge in which dialysis iseffected is removed from the machine between treatments, a sterilisationcartridge is inserted into the machine through which any residual waterin the machine between treatments is circulated as part of the closedloop circuit. Preferably the cartridge has an internal passage way whichforms a part of the sterile water loop such that the heated water entersthe cartridge via the sterile connector and returns to the apparatus viaanother connector. More preferably the cleaning cartridge contains afilter element, through which the residual water flows, which removesany particles or contaminants within the closed loop circuit. Thecleaning cartridge preferably has means for accepting a cleaning fluidor tablet that can be used to chemically and/or biologically sterilisethe closed loop circuit.

Preferably, the cartridge in which dialysis is effected is disposable,being thrown away or recycled after a single use such that a newcartridge is used for each treatment. Preferably all functional elementsrequired for the haemodialysis process that are subject to contaminationby blood or waste products or chemicals needed for the process arecontained within said cartridge. Thus, by providing a single usedisposable dialysis cartridge, firstly the need to clean and sterilisethe aforementioned elements is eliminated and secondly there is nodanger of cross-contamination from one patient to the next. Further, themachine, which preferably includes user-actuable control means forcontrolling the haemodialysis process carried out in the cartridge, maybe re-used successively a number of times without the need to clean itbecause of its being operable to maintain, in a sterile condition,residual water contained in it after completion of a treatment.Accordingly, cleaning operations on the apparatus may be completelyeliminated over an extended period of time, although it may be desirableto clean the water supply elements comprised in the machine, using, forexample, chemical cleaning agents, after it has been used a number oftimes.

In a preferred arrangement the cartridge in which dialysis is effectedis provided with at least one connection means for connection with afluid additive supply whereby an additive, for example bicarbonate orbicarbonate solution, is supplied directly to said cartridge foradmixture to the sterile water thereby forming dialysate solution,without contacting any non disposable parts of the apparatus.Alternatively any fluid additives required for the treatment may becontained within the cartridge.

According to a third aspect of the present invention there is provided acleaning cartridge having a water inlet, a water outlet and a flowpaththerebetween, said cartridge being adapted for releasable connection toa machine as described above and forming a part of a closed loopsterilisation circuit of said machine.

Preferably the cleaning cartridge contains a filter element, throughwhich the residual water flows, which removes any particles orcontaminants within the closed loop circuit. More preferably thecleaning cartridge has means for accepting a cleaning fluid or tabletthat can be used to chemically and/or biologically sterilise the closedloop circuit.

According to a fourth aspect of the invention there is provided acartridge for releasable connection to a machine so as to provideapparatus as defined above.

A preferred machine and cartridge of the invention comprise, incombination, a number of novel and inventive features as are describedbelow with reference to the accompanying drawings, but it is to beunderstood that a machine and/or cartridge of the invention may compriseany one or more of those features.

Embodiments of the invention will now be described by way of exampleonly with reference to the following, largely diagrammatic, drawings inwhich:

FIG. 1 is a front perspective view of the haemodialysis apparatusshowing the re-usable machine and disposable cartridge separate from oneanother,

FIG. 2 is a rear perspective view of the machine shown in FIG. 1,

FIG. 3 is a schematic flow diagram of the haemodialysis process carriedout by the apparatus of FIG. 1,

FIG. 4 is a perspective view of one embodiment of a cartridge with aninternal dialysis filter,

FIG. 5 is a perspective view of an alternative cartridge having anexternal dialysis filter,

FIG. 6 is an exploded perspective view of a cartridge,

FIG. 7 is a cross-sectional view of a typical cartridge pumping element,

FIGS. 8 and 8 a are cross-sectional views of a typical pressuremeasurement element of a cartridge,

FIG. 9 is a perspective view of a close-up of part of the machineshowing the platens;

FIGS. 10, 11 and 12 are cross-sectionional views of a sterile wateroutlet incorporating a flush valve;

FIG. 13 is a schematic diagram of an apparatus in accordance with theinvention having a closed loop water circuit passing through theplatens; and

FIG. 14 is a schematic diagram of an apparatus in accordance with theinvention including a cleaning cartridge.

Referring to FIG. 1, a haemodialysis system is shown which comprises amachine 1 containing a slot 2 adapted to accept and retain therein acartridge 4, and an operator interface 3. The combination of machine andcartridge together, when connected to a patient's circulatory system,perform an extracorporeal haemodialysis process on the patient's bloodbefore returning it to the patient. The operator interface 3 bothpermits control of the dialysis functions, and provides status andwarning information as required.

Referring to FIGS. 1 and 2 when the cartridge 4 is inserted into theslot 2 of the machine 1, an aperture 8 at the rear of the machineprovides access to couple a drain tube 7 and one or more supplementarysupply tubes 6 a, 6 b directly to the rear of the cartridge 4. The tubes6 a, 6 b draw supplementary additives from containers 5 a, 5 b which areshown mounted under the machine 1. An external deionised water supplypipe 9 connects directly to the machine through water inlet 10. Arterialand Venous blood tubes 43, 44 already attached to the cartridge 4 permitconnection of the dialysis system to the patient's blood system.

FIG. 3 shows a fluid flow schematic diagram of the dialysis system, thegeneral nature of which will be familiar to those skilled in the art ofhaemodialysis. The fluid circuit components 10 to 25 incorporated in themachine part of the system are only exposed to the de-ionised watersupply, and do not suffer any contamination from the dialysis process.De-ionised water enters the machine at water inlet 10 incorporating anon-return valve 11 and flows through filter 12, pressure regulator 14,and on/off solenoid 15. A low pressure switch 13 stops the process ifwater supply pressure falls below a preset minimum acceptable level. Amaster flow sensor 16 forms part of the water flow control system. Thewater is preheated in heat exchanger 17, and heated to eighty fivedegrees centigrade by heater 18, controlled by sensor 19. Heating thewater to this temperature is sufficient to destroy any bacteria and ormicro-organisms in the water. After passing through the de-aerationsystem 20, the water is cooled in heat exchanger 17, before passing topump 22. To avoid the need for a supplementary heater in the cartridge,a by-pass valve 21 is adjusted by the control system to provide anoutput temperature, as sensed by temperature sensor 23, of approximately37° C. from the machine to the cartridge 4. If there is a temperaturedrop of the process fluid within the cartridge before the process fluidenters the dialysis filter 38 then the temperature of the water exitingthe machine may be higher than 37 degrees centigrade such that, takingthe temperature drop into consideration, the water is at 37 degreescentigrade when it enters the dialysis filter 38. The water leaves themachine 1 at sterile water outlet 26 and enters the cartridge 4. Thesterile outlet 26 is designed to close off, or be closed off, when thecartridge 4 is decoupled from the machine 1. When there is no cartridge4 present, recirculation control valve 25 is opened, and water flowsthrough the recirculation loop 24, and no new water enters the system.As a result the temperature of the whole water loop rises to at leastabout 85° C., maintaining the sterility of the machine 1 water system.Connectors 10 and 26 are designed such that water flushes all thecontact areas to eliminate any bacterial growth.

Referring again to FIG. 3, the cartridge 4 comprises two separate fluidpaths, one for the dialysis fluid, and one for the patient's blood.Water enters the cartridge from the machine at connector 26 and is mixedwith a predetermined amount of supplementary additive, e.g. bicarbonate,in mixer 28. The supplementary additive is supplied from container 5 aby pump 27. Correct ratio of supplementary additive is determined bycontrolling pump 27, but is also checked by temperature 29 andconductivity 30 measurements. A secondary flow sensor 31 may be used toconfirm the flow rate of the mixture. Similarly, a second supplementaryadditive, e.g. acetate, can be added in precise amounts from container 5b through pump 32, mixer 33, temperature sensor 34, conductivity sensor35, and tertiary flow sensor 36. The fluid mixture passes through abalancing and ultrafiltration system 37, before entering the dialyser38. The waste fluid from the dialyser passes through flow measurementstation 39, pressure sensor 40 and blood leak detection unit 41, beforeentering the balancing unit 37, after which it passes via connector 42on the cartridge 4 direct to drain line 7.

The extracorporeal circuit will be familiar to those skilled in the artof haemodialysis, and is shown set up for twin needle dialysis. Bloodfrom the patient enters the cartridge via arterial tube 43 and itspressure is measured by sensor 45 before it enters the circulation pump46. Anti clotting agent such as Heparin is then added by dosing unit 47,prior to the dialyser 38. The cleansed blood leaving the dialyser againhas a pressure measurement 48, before entering an air detector section49. The blood is then returned to the patient via a venous clamp 50, andthe venous tube 44.

It will be appreciated that at the end of the treatment, extracting thecartridge 4 from the machine 1 removes all contaminated flow passagesand components, leaving the machine 1 in a clean and sterile condition,a condition that may be maintained by recirculating and heating residualwater in the machine 1 as described earlier. The need for subsequentlycleaning and sterilising the machine after each treatment is therebyeliminated, although it may be desirable from time to time to carry themout.

Turning now to the cartridge, FIG. 4 is a view of one embodiment of thecartridge 4 in which the dialyser 38 filter elements are incorporatedwithin the cartridge. Water connector 10 engages with the water supplyline (not shown) within the machine on insertion, and connector 42 forthe drain 7 and the supplementary additive supply tubes 6 a/b, areaccessed directly at the rear of the cartridge. The cartridge isprovided with Arterial 43 and Venous 44 tubes for connection to thepatient's circulatory system.

FIG. 5 is a view of an alternative embodiment of the cartridge 4 inwhich the dialyser 38 is separate from the cartridge, and is of aproprietary commonly available design. In this embodiment, the dialyseris supplied separately, and is attached to the cartridge 4 at a sterilelocation, immediately prior to inserting the cartridge in the machine 1.

The basic construction of the cartridge is illustrated, as an explodedperspective view, in FIG. 6. A central planar core 51, which ispreferably a plastic moulding, has upstanding walls 52 which define flowpassages and cavities for the pumping, valving and sensing elements ofthe process. Flexible films 53, 54 cover the front and rear faces of thecore 51, and are sealably attached to at least the perimeter of the core51.

A key feature of the design of the cartridge 4 shown in FIG. 6 is theinterface between the machine 1 and the cartridge 4 whereby theactuating means for operating the valving and pumping elements, and thetransmitters and receivers for sensing are all contained in the machineside of the interface, and operate on the elements within the cartridgeby way of the flexible films.

FIG. 7 illustrates the operation of a typical cartridge pumping element.Valve elements 55 and 56 are formed in the cartridge core 51, togetherwith pumping chamber 57. These are all covered by film 53. Actuatingmeans situated in the machine cooperate with these elements to displacethe film to perform valve and pumping actions. In the embodiment shown,fluid at high and low pressure is admitted sequentially to the filmareas above elements 55, 56 and 57. By opening and closing the inletvalve 55, and the outlet valve 56 while displacing the film 53 overpumping chamber 57 in an appropriate sequence, fluid in the cartridge isdisplaced from entry flow passage 58 to exit passage 59.

FIGS. 8 and 8 a illustrate a pressure measuring element. A chamber 60 isformed in the core 51 in a flow passage. The film 53 covering thischamber acts as a diaphragm, and is acted upon by the pressure of thefluid in the passage. A force transducer 61 mounted within the machinemeasures the force on the diaphragm, from which the pressure can becalculated.

Referring to FIG. 9 the apparatus is shown with a fixed platen 61 and amovable platen 62 between which the cartridge is inserted and held. Inoperation the cartridge 4 is placed in position and the movable platen62 is pivoted into place. It is then clamped to hold the cartridge 4 insealing contact with the fixed platen 61. The clamping is performed byactuator means (not shown) which are attached to the fixed platen.Alternatively of course simple mechanical clamping means could be used.The fixed platen 61 has provided in its surface a number of depressions63 which align with pumps 64 and valves 65 on the cartridge 4 to controlthe flow of fluid therethrough. The machine 1 has pressure and vacuumpumps (not shown) and associated valving to provide a supply of pressureor vacuum to the various depressions 66. The pressure and vacuum causesthe flexible membrane (53, FIG. 6) of the cartridge 4 to be displaced toopen or close valves or to pump fluid through the fluid circuit of thecartridge 4. The fluid circuit of the cartridge 4 is as describedherein, in particular as described in reference to FIG. 3. A sterilewater outlet 65 from the machine is provided in the fixed platen 61through which sterile water from the machine 1 passes to enter thecartridge 4. Referring now also to FIGS. 10 to 12 details of the sterileconnector are shown. The connector is situated in the fixed platen 61and comprises an actuator 67 and a plunger 68. The plunger 68 is locatedin a bore 69 in the platen 61 such that when the connector 66 is in itsclosed position in which there is no fluid flow through the connector 66to a cartridge 4, the plunger 68 sits such that it is flush with thesurface of the platen 61. Being flush the platen 61 can easily beswabbed before treatment commences with cleaning fluids, for exampleantibacterial agents. The bore 69 and the plunger 68 are both providedwith a slight taper such that a good sealing face is achieved betweenthem. The connector 66 may form a seal by using precision sized parts oralternatively an o-ring or other compliant seal material may bepresented in the bore to prevent any fluid passing between the bore andthe plunger 68. FIG. 10 shows a connector 66 in a closed position, i.e.the position the connector would assume when a cartridge 4 is not inplace and no fluid flow therethrough is required and FIG. 11 shows aconnector 66 in an open position whereby fluid may pass through it. Thecartridge has a compliant seal means surrounding the point of entry ofsterile water such that when presented to the sterile connector 66 andclamped in place a seal is made between the cartridge 4 and the platen61 surrounding the connector 66 preventing leakage of the sterile water.

Referring now to FIG. 12, a connector 66 is shown that additionally thefunctionality of the recirculation control valve (25 FIG. 3) to enablethe sterile water to be circulated through a closed loop when theconnector 66 is in its closed position. The connector comprises aplunger 70 slideable in a bore 71, in the platen 61, said plunger 70having two internal passageways 72, 73. The plunger 70 is movablebetween a first position in which water can flow from an inlet passage74 through passageway 72 and out through the connector 66 to a cartridge4 and a second position, in which the water flowing through the inletpassageway 74 passes through the plunger and exits through an outletpassageway 75 to recirculate through the sterilising means (not shown).O-rings 76 are provided to prevent passage of water between the plunger70 and the platen 61. When the plunger 70 is in its second position itsend face 77 is flush with the surface 78 of the platen 61. When usedthis connector negates the necessity of separate valve 25 in the circuitdiagram shown in FIG. 3.

Referring to FIG. 13 a schematic diagram of the machine is shown. Themajority of the fluid circuit for the machine is the same as describedin reference to FIG. 3. A sterile connector 66 is provided at the fixedplaten 61. The connector is of the sort as described above withreference to FIGS. 10 and 11. When there is no cartridge between theplatens 61, 62 the movable platen 62 moves into position adjacent toplaten 61 and is clamped thereto making sealing contact therewith.Platen 62 has an internal flowpath therethrough which allows water toflow through the connector 66 through the flowpath 79, back into platen61 and rejoin the sterilisation circuit of the machine. In this manner,when not being used to perform dialysis, i.e. when there is no cartridgepresent, the water may be recirculated through a closed loop circuitwithin the machine allowing the temperature to raise to approximately 85degrees centigrade thereby maintaining the water in a sterile condition.

Referring to FIG. 14 a schematic diagram of an apparatus is showncomprising the machine 1 and a cleaning cartridge 80. The flowpath ofthe machine is identical to that described in reference to FIG. 13 butinstead of circulating the water through the movable platen to maintainit in a sterile condition when there is no cartridge in place, thecleaning cartridge 80 is positioned between the platens and clamped intoplace such that water circulates thorough the cleaning cartridge 80 andback into the machine 1, rejoining the sterilisation circuit of themachine 1. Within the cleaning cartridge 80 there is a filter 81 toremove any solid or particulate matter that may get in the circuit whenchanging from dialysis to cleaning cartridge, and cleaning chemicals 82to chemically clean the inside of the water circuit.

1-39. (canceled)
 40. A mixing apparatus for mixing a dialysis solutionfor use in an extracorporeal dialysis process, the apparatus comprising:a water treatment circuit and a dialysis solution mixer cartridge, thecartridge being releasably received on the apparatus, the watertreatment circuit comprising: a purified water inlet, which isconfigured to receive purified water from a purified water supply; asteriliser downstream of the purified water inlet configured tosterilise the purified water from the purified water inlet; and asterile water outlet downstream of the steriliser configured to supplysterile purified water to the dialysis solution mixer cartridge; whereinwater remaining in the water treatment circuit after completion of anextracorporeal dialysis process is residual water, and the watertreatment circuit recycles the residual water in a closed loop throughthe steriliser so as to maintain the residual water in a sterilecondition without passing the residual water through a purifier.
 41. Themixing apparatus according to claim 40, wherein the sterilizer comprisesa heater for heating the water to an elevated temperature at which atleast micro-organisms and bacteria within the water are destroyed. 42.The mixing apparatus according to claim 41, wherein the water is heatedto at least 85 degrees centigrade.
 43. The mixing apparatus according toclaim 41, wherein said mixing apparatus is provided with a heatexchanger to cool the water, prior to its supply to the cartridge, tosubstantially human body temperature.
 44. The mixing apparatus accordingto claim 40, further comprising a valve for preventing water fromexiting the sterile water outlet when no cartridge is present.
 45. Themixing apparatus according to claim 40, further comprising two platens,at least one of which is movable in relation to the other, adapted toreceive and hold the cartridge.
 46. The mixing apparatus according toclaim 45, wherein said platens comprise means for actuating featuresembodied in the cartridge.
 47. The mixing apparatus according to claim40, further comprising two platens, at least one of which is movable inrelation to the other, adapted to receive and hold the cartridge, andwherein one of said platens comprises the sterile water outlet, thesterile water outlet comprising an outlet valve, when in a firstposition presenting a flush surface and preventing water from exitingthe sterile outlet, and when in a second position forming an outlet inthe face of said one platen allowing the sterile water to passtherethrough into the cartridge.
 48. The mixing apparatus according toclaim 47, wherein when the outlet valve is in its first positionresidual water within the mixing apparatus is prevented by said outletvalve from exiting the sterile water outlet, and is circulated aroundsaid closed loop within said apparatus, said closed loop passing thewater through the sterilizer, thereby maintaining the residual water ina sterile condition.
 49. The mixing apparatus according to claim 40,further comprising two platens, at least one of which is movable inrelation to the other, adapted to receive and hold the cartridge, andwherein the sterile water outlet is located in one of the platens and,when a cartridge is not between said platens, the platens sealinglyengage against one another such that the water exits said sterile wateroutlet and is circulated through the platens and through the sterilizerin said closed loop within said apparatus, thereby maintaining theresidual water in a sterile condition.
 50. An apparatus for performinghemodialysis of a patient's blood, the apparatus comprising: a) themixing apparatus according to claim 40; and b) the cartridge beingconnectable by tubing to the patient's blood circulatory system.
 51. Theapparatus according to claim 50, wherein the sterilizer comprises aheater for heating the water to an elevated temperature at which atleast micro-organisms and bacteria within the water are killed.
 52. Theapparatus according to claim 51, wherein when the apparatus is notperforming hemodialysis of a patient's blood the residual water iscirculated around said closed loop circuit at an elevated temperature,thereby maintaining the residual water in a sterile condition.
 53. Theapparatus according to claim 51, wherein the water is heated to at least85 degrees centigrade.
 54. The apparatus according to claim 51, wherein,subsequent to heating the water to sterilize it, said apparatus isprovided with a heat exchanger to cool the water to substantially humanbody temperature.
 55. The apparatus according to claim 54, wherein thewater is cooled to substantially human body temperature within themixing apparatus prior to said water exiting the mixing apparatus viathe sterile outlet.
 56. The apparatus according to claim 51, wherein thewater exits the sterile outlet at an elevated temperature and is cooledto substantially human body temperature within the cartridge.
 57. Theapparatus according to claim 50, wherein when the cartridge isdisconnected from the mixing apparatus, the residual water within themixing apparatus is prevented by a valve from exiting the sterile wateroutlet, and is circulated around a closed loop within said mixingapparatus and said closed loop passing the water through the sterilizer,thereby maintaining the residual water in a sterile condition.
 58. Theapparatus according to claim 50, wherein the mixing apparatus comprisestwo platens, at least one of which is movable in relation to the other,in between which the cartridge is held during use.
 59. The apparatusaccording to claim 58, wherein the cartridge comprises pumps and valvesfor controlling one or more fluid within the cartridge and said platenscomprise means of actuating said pumps and valves.
 60. The apparatusaccording to claim 50, wherein the mixing apparatus comprises twoplatens, at least one of which is movable in relation to the other, inbetween which the cartridge is held during use, and wherein the sterilewater outlet comprises an outlet valve which, when said outlet valve isin a closed position presents a flush surface with one of said platensand prevents water from exiting the sterile outlet and a wherein whensaid outlet valve is in an open position, an outlet is formed in theface of said one platen allowing the sterile water to pass therethroughinto the cartridge.
 61. The apparatus according to claim 60, whereinwhen the outlet valve is in its first position residual water within themixing apparatus is prevented by said outlet valve from exiting thesterile water outlet, and is circulated around a closed loop within saidmixing apparatus, said closed loop passing the water through sterilizer,thereby maintaining the residual water in a sterile condition
 62. Theapparatus according to claim 50, wherein the mixing apparatus comprises:two platens, at least one of which is movable in relation to the other,in between which the cartridge is held during use; and wherein thesterile water outlet is located in one of the platens and, when thecartridge is not connected to said mixing apparatus, the platenssealingly engage against one another such that the water exits saidsterile water outlet and is circulated through the platens and throughthe sterilizer in a closed loop within said mixing apparatus, therebymaintaining the residual water in a sterile condition.
 63. The apparatusaccording to claim 50, wherein the mixing apparatus comprises twoplatens, at least one of which is movable in relation to the other, inbetween which the cartridge is held during use, and wherein uponinsertion of the cartridge between the two platens, the sterile waterconnector interfaces with an edge of the cartridge.
 64. The apparatusaccording to claim 50, further comprising a closed loop circuit and asterilization cartridge and wherein, when the cartridge in whichdialysis is effected is removed from the mixing apparatus betweentreatments, said sterilization cartridge is inserted into the mixingapparatus through which any residual water in the mixing apparatusbetween treatments is circulated as part of the closed loop circuit. 65.The apparatus according to claim 64, wherein the sterilization cartridgehas an internal passage way which forms a part of the sterile water loopsuch that residual water enters the sterilization cartridge via a firststerile connector and returns to the apparatus via a second connector.66. The apparatus according to claim 64, wherein the sterilizationcartridge contains a filter element, through which the residual waterflows, which removes any particles or contaminants within the closedloop circuit.
 67. The apparatus according to claim 64, wherein thesterilization cartridge has a receptacle for accepting a cleaning fluidor tablet that can be used to chemically and/or biologically sterilizethe closed loop circuit.
 68. The apparatus according to claim 50,wherein the cartridge in which dialysis is effected is disposable and isprovided with at least one connector for connection to a fluid additivesupply whereby an additive is supplied directly to said cartridge foradmixture to the sterile water thereby forming dialysate solution, saiddialysate solution contacting only the disposable cartridge of theapparatus.
 69. The apparatus according to claim 50 to wherein thecartridge in which dialysis is effected has contained within saidcartridge, fluid additives for admixture to the sterile water to formdialysate solution.